Non-cooperative Sources Research Articles

A Compressed-Sensing System for Radio Spectrum Monitoring and Localization of Noncooperative Sources

A Compressed-Sensing System for Radio Spectrum Monitoring and Localization of Noncooperative Sources

Reflection-enabled HDOP-weighted underwater acoustic passive localization with a small aperture array

This paper addresses the localization problem of a noncooperative source in the multipath-rich environment. Unlike conventional schemes that only use the line-of-sight (LOS) and the once-surface-reflected (S1B0) path, the proposed scheme utilizes the complete spatial diversity of all multipaths by quantifying their positioning confidence. In the proposed scheme, all the measurement metrics (angle, relative delay and amplitude) extracted from multipath arrival structure, are combined to achieve localization with a small aperture array.Specifically, we first propose an algorithm for extracting multipath arrival structure based on spatial time-frequency analysis of underwater multipath signals. In this algorithm, each path is iteratively extracted, and the extraction error is close to the Cramér–Rao lower bound (CRLB). Then, the obtained CRLB is used to derive horizontal dilution of precision (HDOP) to quantify the positioning confidence of each path. Finally, the source location is estimated from an optimal HDOP-weighted multipath localization algorithm that assigns different weights to the LOS path and non-line-of-sight (NLOS) paths.Statistical-channel-model-based simulations and lake trial corroborate that the proposed scheme reduces the localization error by at least 128% compared with angle-only, relative-delay-only, and conventional hybrid metrics localization schemes.Index Terms--Underwater acoustic passive localization; Multipath arrival structure; Horizontal dilution of precision; Hybrid metrics.

Reconfigurable Intelligent Surface-Aided Emitter Localization

Localization of radio-frequency (RF) transmitters using time difference of arrival (TDOA)-based methods is one of the conventional passive techniques that admits noncooperative source position finding, but suffers from challenging requirements such as precise intersensor synchronization and high-throughput transmission data links. A tradeoff governing the TDOA systems is in the sensor placement configuration. The more distance the sensors are placed, the more accurate localization is carried out, while the cost for the synchronization and data link increases, at the same time. In this work, a novel reconfigurable intelligent surface (RIS)-aided localization system is proposed that enjoys precise location accuracy while reducing the required expenses. The study reveals that the new setup, utilizing the beam-scanning property of the RIS sensors, improves the localization algorithm and outperforms the conventional approach. Also, comparisons with Cramér Rao lower bound (CRLB) are provided, which confirms the efficiency of the proposed method. Several numerical examples indicate the effectiveness of the proposed method, especially in a low signal-to-noise ratio (SNR) regime.

Direct Position Determination for Noncooperative Source with Fast Moving Receivers

The problem of position estimation for a noncooperative source has always been widely discussed in the field of wireless communication. Direct position determination (DPD) for a noncooperative source with fast moving receivers is discussed in this paper. The sinc function is used to reconstruct the signals, which is an important step in DPD for wideband signals. A DPD method based on the baseband signal is proposed which is more practical in communication signal with high carrier frequency. And based on the proposed DPD method, a DPD method for multiple noncooperative stationary sources by single-channel receivers is presented. In order to evaluate the performance of the proposed DPD method, the Cramér-Rao lower bound (CRLB) for DPD based on baseband signal is derived. Several numerical investigations are carried out to evaluate the performance of the proposed method.

Experimental Validation of a Microwave Imaging Method for Shallow Buried Target Detection by Under-Sampled Data and a Non-Cooperative Source.

In microwave imaging, it is often of interest to inspect electrically large spatial regions. In these cases, data must be collected over a great deal of measurement points which entails long measurement time and/or costly, and often unfeasible, measurement configurations. In order to counteract such drawbacks, we have recently introduced a microwave imaging algorithm that looks for the scattering targets in terms of equivalent surface currents supported over a given reference plane. While this method is suited to detect shallowly buried targets, it allows one to independently process all frequency data, and hence the source and the receivers do not need to be synchronized. Moreover, spatial data can be reduced to a large extent, without any aliasing artifacts, by properly combining single-frequency reconstructions. In this paper, we validate such an approach by experimental measurements. In particular, the experimental test site consists of a sand box in open air where metallic plate targets are shallowly buried a (few ) under the air/soil interface. The investigated region is illuminated by a fixed transmitting horn antenna, whereas the scattered field is collected over a planar measurement aperture at a fixed height from the air-sand interface. The transmitter and the receiver share only the working frequency information. Experimental results confirm the feasibility of the method.

Subsurface Detection of Shallow Targets by Undersampled Multifrequency Data and a Non-Cooperative Source

Imaging buried objects embedded within electrically large investigation domains can require a large number of measurement points. This is impractical if long data acquisition time cannot be tolerated or the system is conceived to work at some stand-off distance from the air/soil interface; for example, if it is mounted over some flying platform. In order to reduce the number of spatial measurements, here, we propose a method for detecting and localizing shallowly buried scattering targets from under-sampled far-field data. The method is based on a scattering model derived from the equivalence theorem for electromagnetic radiation. It exploits multi-frequency data and does not require that the transmitter and receivers are synchronized, making the source non-cooperative. To provide a benchmark against which spatial data have to be reduced, first, the number of required spatial measurements is examined by analyzing the properties of the relevant scattering operator. Then, since under-sampling data produces aliasing artifacts, frequency diversity (i.e., multi-frequency data) is exploited to mitigate those artifacts. In particular, single-frequency reconstructions are properly fused and a criterion for selecting the frequencies to be used is provided. Numerical examples show that the method allows for satisfactory target transverse localization with a number of measurements that are much less than the ones required by other methods commonly used in subsurface imaging.

Position and Velocity Estimation of a Non-Cooperative Source From Asynchronous Packet Arrival Time Measurements

We tackle the problem of identifying the trajectory of a moving radio source from Time of Arrival (TOA) measurements collected by a set of cooperating receivers. The considered system is completely asynchronous: nodes clocks are affected by unknown time and frequency offsets, and no control is exerted over packet transmission times. In the proposed solution, the receiver clock offset terms are estimated from TOA measurements on packets originated by non-cooperative reference transmitters, possibly but not necessarily coincidental with reference receivers. Transmission time ambiguity is resolved by exploiting the redundancy associated to the reception of the same packet at multiple receivers. A distinguishing feature of the proposed solution is that it seeks to identify the parameters of the trajectory as a whole, rather than the individual points of transmission as done in traditional point-based approaches. This allows the effective exploitation of TOA measurements collected in lossy scenarios, where the generic packet is received by a smaller subset of the available receivers (at least two). For the problem at hand, we provide distinct estimators based on TOA and Time-Difference of Arrival (TDOA) and prove their equivalence. Numerical results from simulations and from a real WiFi testbed are provided to validate the effectiveness of the proposed method.

Parameter state estimation for bistatic sonar systems

The use of autonomous underwater vehicles (AUVs) cooperating in a network for anti-submarine warfare surveillance operations is of topical interest. Each AUV has to localise and track targets (submarines) robustly and precisely. This can be realised by a bistatic sonar configuration. The precise knowledge of the bistatic system parameters is mandatory for target tracking. These are in particular the positions of the acoustic sources, transmission times, and the position and heading of the AUV sonar sensor. However, these parameters often are not precisely known, e.g. for non-cooperative acoustic sources or due to navigation uncertainties of the AUV. Therefore, the authors consider the inverse problem, i.e. they estimate the bistatic system parameters by exploiting sonar echoes from known stationary `targets' like wrecks or small islands. Their implementation of the estimation method is based on the multihypothesis tracking technique. Results are discussed for two applications: The first one is estimation of the parameters of a non-cooperative source. The second application focuses on the estimation of the receiver parameters; in particular they show that their approach can be used to increase robustness of AUV navigation. Their algorithms are tested with simulated and real data recorded by the Centre for Maritime Research and Experimentation.

Single-frequency subsurface remote sensing via a non-cooperative source

ABSTRACTThe problem of detecting buried scatterers from their scattered field collected under a remote arrangement (i.e. with the sensors deployed at some stand-off distance from the air/soil interface) is considered. A new imaging method that does not require the knowledge of the incident field, information about the transmitting antenna position or timing is proposed. More in detail, the detection problem is cast as the reconstruction of the support of the equivalent surface currents (located at the air/soil interface), which the scattered field can be ascribed to. To this end, a single-view/multistatic configuration, which also reduces the radar system’s cost and complexity, can be employed. It is remarked that the proposed method does not allow to retrieve the scatterers’ depth. Therefore, it is conceived for all those situations where depth is of minor importance or when it is a priori known that the scatterers reside just beneath to the air/soil interface. This is the case, for example, in mine or unexploded improvised device detection where the primary aim is to detect the buried ordnances and locate them transversally. In these cases, the need for a frequency band can be relaxed as well, so that reconstructions can be achieved also in the single-frequency limit case. The latter is clearly a further advantage in that it simplifies the imaging system. The proposed method is checked against half-space synthetic data. The paper also includes some experimental results with data collected under free-space controlled laboratory conditions that can be considered as a proof of concept.

The interrogation game

While there is widespread debate about techniques for obtaining information from non-cooperative sources, there is little research concerning the efficacy of different methods. We introduce the ‘Interrogation Game’ as a simple model of the information a source will provide when faced with either (1) an interrogator using coercive techniques or (2) an interrogator offering rewards. The model demonstrates that coercive interrogation results in a very slight increase in accurate information from knowledgeable sources, but much more inaccurate information from ignorant sources. In short, when ignorant group members refuse to provide information, this increases the inequality of payoffs among group members under coercion while the same behavior – truthfully revealing ignorance – decreases the inequality of payoffs under reward. If ignorant detainees have concern for the payoffs of their other group members, they will admit their ignorance in reward, but not coercion. We test the model with a group-based experiment. As the model predicts, coercion leads subjects to provide more inaccurate information. Contrary to the model’s expectations, however, accurate information is almost equally likely in the coercion and reward treatments.

On Capacity Scaling of Multi-Antenna Multi-Hop Networks: The Significance of the Relaying Strategy in the “Long Network Limit”

The sum-capacity <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex Notation="TeX">$C$</tex></formula> of a static uplink channel with <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$n$</tex> </formula> single-antenna sources and an <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$n$</tex></formula> -antenna destination is known to scale linearly in <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$n$</tex></formula> , if the random channel matrix fulfills the conditions for the Marcenko-Pastur law: if each source transmits at power <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$P/n$</tex></formula> , there exists a positive <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex Notation="TeX">$c_{0}$</tex></formula> , such that <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$\lim_{n \ura{} \infty}C/n=c_{0}$</tex></formula> almost surely. This paper addresses the question to which extent this result carries over to multi-hop networks. Specifically, an <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex Notation="TeX">$L+1$</tex></formula> -hop network with <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$n$</tex> </formula> non-cooperative source antennas, <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$n$</tex></formula> fully cooperative destination antennas, and <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$L$</tex></formula> relay stages of <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$n_{\cal R}$</tex></formula> (cooperative or non-cooperative) relay antennas each is considered. Four relaying strategies are assessed based on the interrelationship between two sequences. For each considered strategy <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">${\rm XF}$</tex></formula> , there exists a sequence <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$(c_{L}^{\rm XF})_{L=0}^{\infty}$</tex> </formula> , such that <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$c_{L}^{\rm XF}=\lim_{n \ura{} \infty}R^{\rm XF}_{L}/n$</tex></formula> almost surely, where <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$R^{\rm XF}_{L}$</tex></formula> denotes the supremum of the set of sum-rates that are achievable by the strategy over <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$L\!+\!1$</tex> </formula> hops. This sequence depends on the sequence <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$(P_{L})_{L=0}^{\infty}$</tex> </formula> , where <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex Notation="TeX">$P_{L}$</tex></formula> corresponds to the power of the source stage and each of the relay stages in an <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$L\!+\!1$</tex></formula> -hop network. Results are summarized as follows: <orderedlist continuation="restarts" numeration="bullet" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <listitem><para>Decode &amp; forward (DF): For <formula formulatype="inline"><tex Notation="TeX">$n_{\cal R}=n$</tex></formula>, <formula formulatype="inline"><tex Notation="TeX">$c^{\rm DF}_{L}$</tex></formula> is constant with respect to <formula formulatype="inline"> <tex Notation="TeX">$L$</tex></formula>, if also <formula formulatype="inline"><tex Notation="TeX">$P_{L}$</tex></formula> is constant with respect to <formula formulatype="inline"> <tex Notation="TeX">$L$</tex></formula>.</para></listitem></orderedlist>

Array Shape Observability From Time Differences of Arrival

In this paper, we study the observability conditions for the relative position of a set of passive sensors from the measured time differences of arrival (TDOA) of signals from a set of noncooperative sources lying in the same plane. The sources are broadband to measure the TDOA and far enough to consider each source is detected in the same line of sight by each sensor. We show that a necessary observability condition is to have at least three sensors and three sources. Then, the sufficient observability conditions are established in this minimal configuration. Finally, we propose an algorithm to compute both sensors' location and the direction of arrival (DOA) of the sources, from the noise-free TDOA.

Doppler synthetic aperture hitchhiker imaging

In this paper we consider passive airborne receivers that use backscattered signals from sources of opportunity transmitting single-frequency or ultra-narrowband waveforms. Because of its combined passive synthetic aperture and the single-frequency nature of the transmitted waveforms, we refer to the system under consideration as Doppler synthetic aperture hitchhiker (DSAH). We present a novel image formation method for DSAH. Our method first correlates the windowed signal obtained from one receiver with the windowed, filtered, scaled and translated version of the received signal from another receiver. This processing removes the transmitter-related variables from the phase of the Fourier integral operator that maps the radiance of the scene to the correlated signal. Next, we use microlocal analysis to reconstruct the scene radiance by the weighted backprojection of the correlated signal. The image reconstruction method is applicable to both cooperative and non-cooperative sources of opportunity using one or more airborne receivers. It has the desirable property of preserving the visible edges of the scene radiance. Additionally, it is an analytic reconstruction technique that can be made computationally efficient. We present numerical simulations to demonstrate the performance of the image reconstruction method and to verify the theoretical results.

Synthetic Aperture Hitchhiker Imaging

We introduce a novel synthetic-aperture imaging method for radar systems that rely on sources of opportunity. We consider receivers that fly along arbitrary, but known, flight trajectories and develop a spatio-temporal correlation-based filtered-backprojection-type image reconstruction method. The method involves first correlating the measurements from two different receiver locations. This leads to a forward model where the radiance of the target scene is projected onto the intersection of certain hyperboloids with the surface topography. We next use microlocal techniques to develop a filtered-backprojection-type inversion method to recover the scene radiance. The method is applicable to both stationary and mobile, and cooperative and noncooperative sources of opportunity. Additionally, it is applicable to nonideal imaging scenarios such as those involving arbitrary flight trajectories, and has the desirable property of preserving the visible edges of the scene radiance. We present an analysis of the computational complexity of the image reconstruction method and demonstrate its performance in numerical simulations for single and multiple transmitters of opportunity.

Application of the multi-cycle estimator of Doppler and TDOA to passively locating targets exploiting non-cooperative transmitters

Abstract By exploiting the cyclostationary property of non-cooperative source signals, the problem of joint time-difference-of-arrival (TDOA) and Doppler estimation is discussed, and the multi-cycle estimator is developed by generalizing the single-cycle estimator. Utilizing a special commercial FM radio as a non-cooperative transmitter, some practical experiments are carried out. The right estimates of TDOA and Doppler of a particular airplane can really be obtained by processing the measurements with the multi-cycle estimation algorithm. Through adding some slowly time-variant white Gaussian noise to the original measurements, some independent Monte Carlo simulations are performed, and the simulation results reveal that the multi-cycle estimator is really superior to the single-cycle estimator and the conventional cross-correlation method.

Blind beamforming/geolocation for wideband-FFHs with unknown hop-sequences

An ESPRIT based adaptive geolocation and blind interference rejection scheme is herein proposed for multiple noncooperative wideband fast frequency-hop (FFH) signals of unknown hop sequences and unknown arrival angles using one electromagnetic vector-sensor. Beamforming weights need no adjustments to accommodate the frequency hops. The sources' polarizational diversity, angular spatial diversity, and temporal characteristics are all exploited. Applications include electronic surveillance and direction finding of noncooperative sources, plus blind cochannel interference rejection in frequency-hop code-division multiple-access (FH-CDMA) wireless communications.